Inlet turning ring seal

ABSTRACT

An improved turning ring seal is provided at the inlet of a turboblower to prevent high pressure fluid from discharging back into the inlet of the impeller. The stationary portion of the seal is provided by an integral curved annular shoulder around the inlet of the casing. The rotating portion of the seal is provided by the inner diameter of the blade shroud.

United States Patent Inventor John A. Marine Palmyra, Pa. App]. No.841,737 Filed July 15, 1969 Patented Mar. 30, 1971 Assignee HauckManufacturing Company Lebanon, Pa.

INLET TURNING RING SEAL 10 Claims, 3 Drawing Figs.

US. Cl 415/174, 415/212 Int. Cl F04d 29/66 Field ofSearch 415/171, 174,111 (B); 103/111 (C)4, 111 (C)2, 111 (C) 3, 111 (C15 References CitedUNlTED STATES PATENTS 9/ 1 935 Meckenstock 9/1958 Pedersen 3/1960Koehringm. 6/1963 Morley et al Primary ExaminerC. J. l-lusarAttorney-Finnegan, Henderson & Farabow ABSTRACT: An improved turningring seal is provided at the inlet of a turboblower to prevent highpressure fluid from discharging back into the inlet of the impeller. Thestationary portion of the seal is provided by an integral curved annularshoulder around the inlet of the casing. The rotating portion of theseal is provided by the inner diameter of the blade shroud.

2 Sheets-Sheet 1 44 FIG. 1

AIR FLOW l8 INVEN'IOR JOHN A. MARINO Jzznegam fe/zdmm (gzyafiowATTORNEYS Patented March 30, 1971 3,572,963

2 Sheets-Sheet 2 INVENTOR JOHN A. MARINO ATTORNEYS TNLET ruhuiuc nrucsnxr.

This invention relates to a ring seal, and more particularly to animproved turning ring seal for use in centrifugal blowers of the typeincluding a casing, and a centrifugal impeller assembly which isenclosed by the casing.

Centrifugal air blowers, and particularly turboblowers, are used toprovide large volumes of relatively low pressure air in numeroussituations, for example as combustion blowers. Because large volumes ofair are handled, smoothly contoured air flow conduits within the blowerare desirable to minimize frictional power losses.

Flow in a radial flow compressor moves from an inlet opening locatedadjacent to the axis of the rotary machine to the outer diameter of theimpeller blades. Since energy is added to the fluid, the pressure of thefluid is greater at the outer diameter of the impeller than at theinlet. Fluid will therefore have a tendency to move from-the higherpressure discharge area back into the inlet of the impeller. Where thisbackflow coming from the discharge area of the impeller intersects thenormal flow into the impeller inlet, significant turbulence occurs inthe inlet flow, which lowers the machine s total efficiency.

While it is possible to machine the blades and the casing to very narrowtolerances, and thus obtain a seal, this precision machining isexpensive and is impractical for prefabricated blower assemblies. Forexample, the running position of the blades would have to be preciselyset during assembly of the blower and carefully maintained during use.

Another problem which exists in providing a seal against backflow of airis that the seal should not interfere with the desired inlet flow of airto the blades. In other words, the seal should not present sharpdiscontinuous surfaces which would block or sharply change the directionof inlet air flow.

The present invention provides a turning ring seal located near thecasing inlet to the impeller that can prevent the return flow of air,and can function without creating an undesirable level of turbulence inthe inlet flow of air.

The invention is used in a centrifugal blower or compressor comprisingan impeller assembly having a hub and a plurality of impeller blades;and a generally disc-shaped casing enclosing the impeller assembly, andincluding an inlet opening extending through one face of the casing andpositioned along the axis of the casing, and a discharge openingpositioned adjacent the outer diameter of the impeller blades. Theinvention provides an improved turning ring seal to prevent backflow ofhigh-pressure air to the inlet opening and is formed by a integralshoulder forming a part of the casing and extending around the perimeterof the inlet opening, the shoulder presenting a convex annular surfacewhich protrudes inwardly of the relatively planar interior wall surfaceof the inlet face of the disc-shaped casing. The rotating portion of theseal is formed by the forward edge of the impeller assembly which ispositioned a small distance fi om the shoulder, the distance being lessthan the distance from the forward edge of the impeller assembly to thecasing to create a zone of high-pressure adjacent the shoulder. The sealthus reduces the flow area and restricts fluid flow from the clearancearea, where the blades must be widely spaced from the casing, to the lowpressure inlet region.

Preferably, the forward edge of the impeller assembly is a rotatingshroud attached to said blades, the shroud comprising an annular platehaving its interior diameter positioned closely adjacent the shoulder.

Preferably, the shoulder is contoured so that from its inner diameterthe shoulder extends axially in the direction of flow and radiallyoutward relative to the blower axis in a smooth curve from the inlet.Thus, the interior portion of the convex annular surface extends axiallyinto thecasing and in a radially outward direction from the axis of thecasing opening.

Preferably, the interior surface of the shoulder is formed of arelatively soft abradable material and the material of construction ofthe blades and the shroud is harder than the soft abradable material sothat the blades and shroud can wear away the shoulder, if the shoulderinitially interferes with rotation of the blades and the shroud.

In the presently preferred form of the invention, the interior surfaceof the shoulder is formed by an elastomeric coating layer which deflectswhen contacted by the impeller blades or the shroud.

The invention consists in the novel parts, constructions, arrangements,combinations, and improvements shown and described. The accompanyingdrawings, which are incorporated in and constitute a part of thisspecification, illustrate one embodiment of the invention and, togetherwith the description, serve to explain the principles of the invention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory, butare not restrictive of the invention.

In the drawing:

FIG. 1 is a fragmented horizontal section illustrating the ring seal ofthis invention installed in a centrifugal blower;

FIG. 2 is a side elevation of the interior wall surface of the inlethalf of the casing of FIG. 1', and

FIG. 3 is a vertical section taken along line 3-3 of FIG. 2.

Referring to the embodiment illustrated in FIG. 1, the turning ring sealof this invention isv shown in a centrifugal air blower that comprises ahub assembly, generally 10, a plurali ty of impeller blades 12 which areattached to the hub assembly, and a disc-shaped casing which enclosesthe hub assembly and the blades. While a fabricated impeller assembly isillustrated it should be realized that the invention can be used withintegrally cast impeller assemblies.

The casing is formed by an inlet shell 16 and an outlet shell 18. Aninlet opening 20 is located along the axis 22 of the discshaped casingand is defined by a bellmouthed wall surface 24 on shell 16. A dischargeopening 26, best seen in FIG. 2, is positioned adjacent the outerdiameter of impeller blades 12.

Hub assembly 10 includes a hub 30 which can be mounted on a power drivenshaft (not shown). A blade retainer 32 and a compression means such as astud and lock nut (not shown) are provided to clamp blades 12 to hub 30.The blades each have a tab 38 on their leading edge, which is clampedbetween the blade retainer and the hub.

A backplate 40 is attached to the hub 30 by bolts 42 and to blades 12 byrivets 44. Backplate 40 thus cooperates with the blades in forming flowchannels for the flow of air through the blower.

In accordance with the present invention, an inlet turning ring seal isprovided by a stationary (nonrotating) curved annular shoulder 50 whichis integral with and extends around the perimeter of the casing inletopening, and presents a convex annular surface 52 which protrudesinwardly of the relatively planar interior wall surface 54 of inletshell 16 of the casing. Shoulder 50 extends around the perimeter ofinlet opening 20, and thus forms an annular surface.

With reference to FIG. I, shoulder .50 is contoured so that from itsinner diameter it extends in the direction of flow and radially outwardrelative to axis 22 in a. smooth curve from the wall surface of theinlet opening. The tip of the convex shoulder is also smoothly curved,as is the juncture of the outer diameter of shoulder 50 and thegenerally planar interior wall surface of inlet shell 16. Thus, shoulder50 besides cooperating to form a seal, provides at its inner portion asmooth curved contour for fluid to follow as its flow direction beginschanging from axial to radial.

In the presently preferred embodiment of the invention, the interiorsurface of shoulder 50 is formed by an elastomeric coating layer whichdeflects when contacted by the impeller blades, or a shroud which isdescribed below. The tip of the convex shoulder can be entirelyelastomer to provide a flaptype lip. An elastomeric surface providesoutstanding re sistance to abrasive particles and thus is a desirablecoating layer for the entire interior surface of shell 16. Suitableeiastomers include polyurethanes such as that sold under the trademarkAdiprene by E. l. duPont De Nemours, and various other synthetic rubberswhich exhibit good abrasion resistance to a small fluid-carried solidparticles, such as sand. it should be realized that such elastomerswhile described as abrasion resistant with respect to smallfluid-carried particles, are softer than, and can be abraded by contactwith metal surfaces, the usual material of construction for the impellerblades and the shroud.

in accordance with the invention, the rotating portion of the inlet sealis provided by the inner diameter of a shroud which is attached to theimpeller blades with its inner diameter positioned closely adjacent theshoulder. As here embodied, and as illustrated in H6. 1, a shroud 56 isattached to the forward edge of impeller blades 12 by rivets 57. Theshroud is annular and generally planar and extends in a radial directionfrom an inner diameter which is approximately equal to the outerdiameter of shoulder 50, to an outer diameter which terminates adjacentthe tip of the blades;

The inner diameter of shroud 56 is axially spaced a small distancebehind the convex tip of shoulder 50 in the flow direction. This spacingis desirable because blade 12, to which the shroud is attached, shouldcurve radially outwardly as it extends axially, to assist in changingthe direction of fluid flow through the impeller.

Generally, the distance between the inner diameter of shroud 56 and theclosest position of shoulder 50 will vary from about 0.20 inches to 0.40inches depending on the pressure differential developed by the impellerassembly.

As illustrated in FIG. 1, shroud 56 is aligned parallel to the planarinterior surface 54 of inlet shell 16. Thus, shoulder 50 which projectsinwardly of surface 54 creates a reduced flow area for the backflow ofair; that is, shoulder 50 is positioned closer to the adjacent portionof the impeller assembly than the spacing of the outer portions of theimpeller assembly from the outer portion of the casing.

While the invention has been illustrated and described in relation to asingle stage blower, it will be realized by those skilled in the artthat the invention can be incorporated in one or more, and preferablyevery stage of a multistage blower.

The need for the present invention and its utility are graphically shownin HO. 1 where arrows represent the direction of air flow in a singlestage centrifugal blower operating at other than its design flow. Asillustrated in FIG. 1, a design requirement for a large runningclearance between the blades 12 and the blower casing permitshigh-pressure air located near the tip of the blades to flow backtowards inlet 20 between the inlet shell 16 and shroud 56. This backflowof air, if permitted to contact the inlet flow of air, createsturbulence which markedly lowers the efficiency of the blower.

The seal provided by shoulder 50 and shroud 56 helps prevent thebackflow of air from interfering with the inlet flow of air. All thereasons why the present seal is effective in reducing the volume ofbackflow and therefore frictional losses in a centrifugal blower are notprecisely known. However, it is believed that a reduced flow areabetween the inner diameter of shroud 56 and shoulder 50 as compared tothe area between wall surface 54 of inlet shell 16 and the outerportions of the shroud creates a restriction which reduces the amount ofsecondary flow able to reenter the inlet as shown in FlG. l.

The preferred elastomeric interior surface layer of inlet casing 16 isdesirably open cast into an open mold with a polyester backing layersubsequently bonded thereto according to the following procedure.

The mold surface which is to be reproduced is first treated with a moldrelease agent appropriate for the elastomer to be used. The elastomer,such as a polyether polyurethane, is then brushed onto the mold surfaceat the appropriate temperature to obtain the required physicalproperties. Urethane for example can be applied at room temperature. Theelastomer is then cured until the exterior surface is just tack free.For example, room cured urethane can be allowed to cure from 12-72hours. If high temperature cures are used, l30 minutes will obtain therequired surface condition for the next step in the process.

Another thin coat of urethane is then similarly applied to the semicuredsurface of the first coat. Immediately, chopped fibers of the materialto be used in reinforcing the plastic resin are deposited onto theliquid urethane surface and mechanically worked into this thin coatingof wet urethane. Fibers of long enough length should be used to entirelycoat the urethane surface and leave ends protruding from the wetsurface. Fibers of l-inch in length have been found to work well.

The surface is next painted or sprayed with a catalyzed liquid resin,such as a polyester, and thoroughly rolled with surface rollers toremove all entrapped air. Plastic resin and reinforcement can then beadded to obtain the required stiffness and strength of the finishedcomposite.

When all required curing is completed, the chopped fibers applied to thewet coat of urethane provide a mechanical linkage between the urethanesurface and the reinforced plastic.

In summary the invention provides a turning ring seal in which therotating portion of the seal is provided by the inner diameter of bladeshroud 56 and the stationary portion of the seal is provided by a curvedannular shoulder 50 which is an integral part of the casing. The innerdiameter of the shroud and the diameter of the shoulder can bemanufactured within a close tolerance without the need for supplementalmachining or finishing operations. The running position of the seal inan assembled centrifugal blower is not dependent on manufacturingtolerances maintained during fabrication and assembly of the rest of themachine. Therefore, an inexpensive 'seal can be obtained by utilizingthis invention.

The invention in its broader aspects is not limited to the specificdetails shown and described and departures may be made from such detailswithout departing from the principles of the invention and withoutsacrificing its chief advantages.

lclaim:

1. In a centrifugal blower comprising an impeller assembly having a huband a plurality of impeller blades; and a generally disc-shaped casingthat encloses the impeller assembly and includes an inlet openingextending through one face of the easing and positioned along the axisof the casing, and a discharge opening positioned adjacent the outerdiameter of the impeller blades, the improvement comprising an improvedturning ring seal to prevent backflow of high pressure air to the inletopening, said seal having: a stationary shoulder which is an integralpart of the casing and extends around the perimeter of the inletopening, said shoulder presenting a convex annular surface whichprotrudes inwardly of the planar interior wall surface of the inlet faceof the disc-shaped casing; and a rotating shroud attached to the blades,said shroud comprising an annular plate having its interior diameterpositioned closely adjacent said shoulder.

2. The invention of claim 1 in which the interior portion of the convexannular surface extends axially into the interior of the casing and in aradially outward direction from the axis of the casing, said directionbeing generally aligned with the flow path of inlet air to the impellerblades to minimize frictional lo es at the inlet opening.

3. The invention of claim 1 in which the interior surface of saidshoulder is manufactured of a relatively soft, abradable material andthe material of construction of the blade and said shroud is harder thansaid soft, abradable material so that the blades and said shroud canwear away said shoulder if said shoulder initially interferes withrotation of the blades and said shroud.

4. The invention of claim 2 in which shoulder is manufactured of arelatively soft, abradable material and the material of construction ofthe blades and said shroud is harder than said soft abradable material,so that the blades and said shroud can wear away said shoulder, if saidshoulder initially interferes with rotation of the blades and saidshroud.

5. The invention of claim 1 in which the surface of said shoulder isformed from an elastomer which deflects when contacted by the blades orsaid shroud.

6. The invention of claim 2 in which the surface of said shoulder isformed from an elastomer which deflects when contacted by the blades orsaid shroud.

7. The invention of claim 1 in which the inner diameter of said shroudis axially spaced a small distance behind the convex tip of saidshoulder in the flow direction.

ing ring seal to prevent back flow of high-pressure air to the inletopening, said seal formed by a stationary shoulder forming a part of thecasing and extending around the perimeter of the inlet opening, saidshoulder presenting a convex annular surface which protrudes inwardly ofthe relatively planar interior wall surface of the inlet face of thedisc-shaped casing; and a rotating forward edge of said impellerassembly, the forward edge of said impeller assembly being positioned adistance from said shoulder which is less than the distance from theforward edge to the relatively planar interior wall surface of the inletface of the disc-shaped casing.

9. The invention of claim 8 in which the interior portion of the convexannular surface extends axially into the interior of the casing and in aradially outward direction from the axis of the casing, said directionbeing generally aligned with the flow path of inlet air to theimpeller'blades to minimize frictional losses at the inlet opening.

10. The invention of claim 8 in which the surface of said shoulder isformed from an elastomer which deflects when contacted by the blades orthe shroud.

1. In a centrifugal blower comprising an impeller assembly having a huband a plurality of impeller blades; and a generally disc-shaped casingthat encloses the impeller assembly and includes an inlet openingextending through one face of the casing and positioned along the axisof the casing, and a discharge opening positioned adjacent the outerdiameter of the impeller blades, the improvement comprising an improvedturning ring seal to prevent backflow of high presSure air to the inletopening, said seal having: a stationary shoulder which is an integralpart of the casing and extends around the perimeter of the inletopening, said shoulder presenting a convex annular surface whichprotrudes inwardly of the planar interior wall surface of the inlet faceof the disc-shaped casing; and a rotating shroud attached to the blades,said shroud comprising an annular plate having its interior diameterpositioned closely adjacent said shoulder.
 2. The invention of claim 1in which the interior portion of the convex annular surface extendsaxially into the interior of the casing and in a radially outwarddirection from the axis of the casing, said direction being generallyaligned with the flow path of inlet air to the impeller blades tominimize frictional losses at the inlet opening.
 3. The invention ofclaim 1 in which the interior surface of said shoulder is manufacturedof a relatively soft, abradable material and the material ofconstruction of the blade and said shroud is harder than said soft,abradable material so that the blades and said shroud can wear away saidshoulder if said shoulder initially interferes with rotation of theblades and said shroud.
 4. The invention of claim 2 in which shoulder ismanufactured of a relatively soft, abradable material and the materialof construction of the blades and said shroud is harder than said softabradable material, so that the blades and said shroud can wear awaysaid shoulder, if said shoulder initially interferes with rotation ofthe blades and said shroud.
 5. The invention of claim 1 in which thesurface of said shoulder is formed from an elastomer which deflects whencontacted by the blades or said shroud.
 6. The invention of claim 2 inwhich the surface of said shoulder is formed from an elastomer whichdeflects when contacted by the blades or said shroud.
 7. The inventionof claim 1 in which the inner diameter of said shroud is axially spaceda small distance behind the convex tip of said shoulder in the flowdirection.
 8. In a centrifugal blower comprising an impeller assemblyhaving a hub and a plurality of impeller blades; and a generallydisc-shaped casing that encloses the impeller assembly and includes aninlet opening extending through one face of the casing and positionedalong the axis of the casing, and a discharge opening positionedadjacent the outer diameter of the impeller blades, the improvementcomprising an improved turning ring seal to prevent back flow ofhigh-pressure air to the inlet opening, said seal formed by a stationaryshoulder forming a part of the casing and extending around the perimeterof the inlet opening, said shoulder presenting a convex annular surfacewhich protrudes inwardly of the relatively planar interior wall surfaceof the inlet face of the disc-shaped casing; and a rotating forward edgeof said impeller assembly, the forward edge of said impeller assemblybeing positioned a distance from said shoulder which is less than thedistance from the forward edge to the relatively planar interior wallsurface of the inlet face of the disc-shaped casing.
 9. The invention ofclaim 8 in which the interior portion of the convex annular surfaceextends axially into the interior of the casing and in a radiallyoutward direction from the axis of the casing, said direction beinggenerally aligned with the flow path of inlet air to the impeller bladesto minimize frictional losses at the inlet opening.
 10. The invention ofclaim 8 in which the surface of said shoulder is formed from anelastomer which deflects when contacted by the blades or the shroud.